Publications

<strong class="journal-contentHeaderColor">Abstract.</strong> Ozone (O₃) is an important secondary pollutant that impacts air quality and human health. Eastern Asia has high regional O₃ background due to the numerous sources and increasing and rapid industrial growth, which impacts the Seoul Metropolitan Area (SMA). However, SMA has also been experiencing increasing O₃ driven by decreasing NO_x emissions, highlighting the role of local, in-situ O₃ production on SMA. Here, comprehensive gas-phase measurements collected on the NASA DC-8 during the NIER/NASA Korea United States-Air Quality (KORUS-AQ) study are used to constrain the instantaneous O₃ production rate over the SMA. The observed NO_x oxidized products support the importance of non-measured peroxy nitrates (PNs) in the O₃ chemistry in SMA, as they accounted for ~49 % of the total PNs. Using the total measured PNs (&Sigma;PNs) and alkyl and multifunctional nitrates (&Sigma;ANs), unmeasured volatile organic compound (VOC) reactivity (R(VOC)) is constrained and found to range from 1.4 &ndash; 2.1 s^-1. Combining the observationally constrained R(VOC) with the other measurements on the DC-8, the instantaneous net O₃ production rate, which is as high as ~10 ppbv hr^-1, along with the important sinks of O₃ and radical chemistry, are constrained. This analysis shows that &Sigma;PNs play an important role in both the sinks of O₃ and radical chemistry. Since &Sigma;PNs are assumed to be in steady-state, the results here highlight the role &Sigma;PNs play in urban environments in reducing net O₃ production, but &Sigma;PNs can potentially lead to increased net O₃ production downwind due to their short lifetime (~1 hr). The results provide guidance for future measurements to identify the missing R(VOCs) and &Sigma;PNs<strong> </strong>production.

During the Tropical Composition, Clouds and Climate Coupling (TC4) experiment that occurred in July and August of 2007, extensive sampling of active convection in the ITCZ region near Central America was performed from multiple aircraft and satellite sensors. As part of a sampling strategy designed to study cloud processes, the NASA ER‐2, WB‐57 and DC‐8 flew in stacked “racetrack patterns” in convective cells. On July 24, 2007, the ER‐2 and DC‐8 probed an actively developing storm and the DC‐8 was hit by lightning. Case studies of this flight, and of convective outflow on August 5, 2007 reveal a significant anti‐correlation between ozone and condensed cloud water content. With little variability in the boundary layer and a vertical gradient, low ozone in the upper troposphere indicates convective transport. Because of the large spatial and temporal variability in surface CO and other pollutants in this region, low ozone is a better convective indicator. Lower tropospheric tracers methyl hydrogen peroxide, total organic bromine and calcium substantiate the ozone results. OMI measurements of mean upper tropospheric ozone near convection show lower ozone in convective outflow. A mass balance estimation of the amount of convective turnover below the tropical tropopause transition layer (TTL) is 50%, with an altitude of maximum convective outflow located between 10 and 11 km, 4 km below the cirrus anvil tops. It appears that convective lofting in this region of the ITCZ is either a two‐stage or a rapid mixing process, because undiluted boundary layer air is never sampled in the convective outflow.

s of Papers Presented at the WMO-IGA C Conference on the Measurement and Assessment of A tmospheric Composition Change, Beij ing, China, 91 3 October, 1 995 , WMO/TD-No. 7 1 0,

Author(s): Kondo, Y; Chen, G; Hudman, R; Jacob, D; Koike, M; Nakamura, K; Takegawa, N; Kita, K; Miyazaki, Y; Blake, DR; Shirai, T; Kawakami, S; Takigawa, M; Akimoto, H; Ogawa, T

Abstract. The atmospheric sulfur cycle plays a key role in air quality, climate, and ecosystems, such as pollution, radiative forcing, new particle formation, and acid rain. In this study, we compare the spatially and temporally resolved measurements from the NASA Atmospheric Tomography (ATom) mission with simulations from five AeroCom III models for four sulfur species (dimethyl sulfide (DMS), sulfur dioxide (SO2), particulate methanesulfonate (MSA), and particulate sulfate (SO4)). We focus on remote regions over the Pacific, Atlantic, and Southern oceans from near the surface to ∼ 12 km altitude range covering all four seasons. In general, the differences among model results can be greater than 1 order of magnitude. Comparing with observations, model-simulated SO2 is generally low, whereas SO4 is generally high. Simulated DMS concentrations near the sea surface exceed observed levels by a factor of 5 in most cases, suggesting potential overestimation of DMS emissions in all models. With GEOS model simulations of tagging emission from anthropogenic, biomass burning, volcanic, and oceanic sources, we find that anthropogenic emissions are the dominant source of sulfate aerosol (40 %–60 % of the total amount) in the ATom measurements at almost all altitudes, followed by volcanic emissions (18 %–32 %) and oceanic sources (16 %–32 %). Similar source contributions can also be derived at broad ocean basins and on monthly scales, indicating the representativeness of ATom measurements for global ocean. Our work presents the first assessment of AeroCom sulfur study using ATom measurements, providing directions for improving sulfate simulations, which remain the largest uncertainty in radiative forcing estimates in aerosol climate models.

Abstract. Recent in situ and satellite measurements suggest a contribution of ~5 pptv to stratospheric inorganic bromine from short-lived bromocarbons. We conduct a modeling study of the two most important short-lived bromocarbons, bromoform (CHBr3) and dibromomethane (CH2Br2), with the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to account for this missing stratospheric bromine. We derive a "top-down" emission estimate of CHBr3 and CH2Br2 using airborne measurements in the Pacific and North American troposphere and lower stratosphere obtained during previous NASA aircraft campaigns. Our emission estimate suggests that to reproduce the observed concentrations in the free troposphere, a global oceanic emission of 425 Gg Br yr−1 for CHBr3 and 57 Gg Br yr−1 for CH2Br2 is needed, with 60% of emissions from open ocean and 40% from coastal regions. Although our simple emission scheme assumes no seasonal variations, the model reproduces the observed seasonal variations of the short-lived bromocarbons with high concentrations in winter and low concentrations in summer. This indicates that the seasonality of short-lived bromocarbons is largely due to seasonality in their chemical loss and transport. The inclusion of CHBr3 and CH2Br2 contributes ~5 pptv bromine throughout the stratosphere. Both the source gases and inorganic bromine produced from source gas degradation (BryVSLS) in the troposphere are transported into the stratosphere, and are equally important. Inorganic bromine accounts for half (2.5 pptv) of the bromine from the inclusion of CHBr3 and CH2Br2 near the tropical tropopause and its contribution rapidly increases to ~100% as altitude increases. More than 85% of the wet scavenging of BryVSLS occurs in large-scale precipitation below 500 hPa. Our sensitivity study with wet scavenging in convective updrafts switched off suggests that BryVSLS in the stratosphere is not sensitive to convection. Convective scavenging only accounts for ~0.2 pptv (4%) difference in inorganic bromine delivered to the stratosphere.

Abstract. Fires emit a substantial amount of non-methane organic gases (NMOGs); the atmospheric oxidation of which can contribute to ozone and secondary particulate matter formation. However, the abundance and reactivity of these fire NMOGs are uncertain and historically not well constrained. In this work, we expand the representation of fire NMOGs in a global chemical transport model, GEOS-Chem. We update emission factors to Andreae (2019) and the chemical mechanism to include recent aromatic and ethene/ethyne model improvements (Bates et al., 2021; Kwon et al., 2021). We expand the representation of NMOGs by adding lumped furans to the model (including their fire emission and oxidation chemistry) and by adding fire emissions of nine species already included in the model, prioritized for their reactivity using data from the FIREX laboratory studies. Based on quantified emissions factors, we estimate that our improved representation captures 72 % of emitted, identified NMOG carbon mass and 49 % of OH reactivity from savanna and temperate forest fires, a substantial increase from the standard model (49 % of mass, 28 % of OH reactivity). We evaluate fire NMOGs in our model with observations from the Amazon Tall Tower Observatory (ATTO), FIREX-AQ and DC3 in the US, and ARCTAS in boreal Canada. We show that NMOGs, including furan, are well simulated in the eastern US with some underestimates in the western US and that adding fire emissions improves our ability to simulate ethene in boreal Canada. We estimate that fires provide 15 % of annual mean simulated surface OH reactivity globally, and exceeding 75 % over fire source regions. Over continental regions about half of this simulated fire reactivity comes from NMOG species. We find that furans and ethene are important globally for reactivity, while phenol is more important at a local level in the boreal regions. This is the first global estimate of the impact of fire on atmospheric reactivity.

Airborne trace gas measurements from Transport and Chemical Evolution over the Pacific (TRACE‐P), Pacific Exploratory Mission (PEM)‐Tropics B, and Intercontinental Chemical Transport Experiment‐North America (INTEX‐NA) experiments are analyzed to examine the major source factors contributing to the observed variabilities of oxygenated volatile organic compounds and cyanides. The positive matrix factorization method is applied to coincident measurements of 11 chemicals including CH 3 OH, CH 3 COCH 3 , CH 3 CHO, C 2 H 2 , C 2 H 6 , i‐C 5 H 12 , CO, CH 3 Cl, and CHBr 3 . Measurements of HCN and CH 3 CN are available for TRACE‐P and INTEX‐NA. We identify major source contributions from the terrestrial biosphere, biomass burning, industry/urban regions, and oceans. Spatial and back trajectory characteristics of these factors are examined. On the basis of TRACE‐P and PEM‐Tropics B data, we find a factor that explains 80–88% of the CH 3 OH variability, 20–40% of CH 3 COCH 3 , 7–35% of CH 3 CHO, and 41% of HCN, most likely representing the emissions from terrestrial biosphere. Our analysis suggested that biogenic emissions of HCN may be significant. Cyanogenesis in plants is likely a major emission process for HCN, which was not fully accounted for previously. Larger contributions than previous global estimations to CH 3 COCH 3 and CH 3 CHO by biomass burning and industry/urban sources likely reflect significant secondary production from volatile organic compound oxidation. No evidence was found for large emissions of CH 3 COCH 3 from the ocean. The oceanic CH 3 CHO contribution implies large regional variations.